1. Field of the Invention
This invention relates in general to fluid flow meters, more particularly to Price Type-AA fluid flow meters, and most particularly to the bucket wheel assembly used in Price Type-AA fluid flow meters.
2. Description of the Related Art
Measurements of water flow are of interest to those in the fields of managing water resources, designing water control structures, or investigating hydrologic systems. Many devices have been designed to measure flow in open channel systems. For many years, the U.S. Geological Survey has employed Price Type-AA fluid flow meters in the field for this purpose.
In operation, the Price Type-AA fluid flow meter employs a bucket wheel assembly that is mounted upon a shaft and rotates in response to fluid flow, generating a signal that is proportional to the fluid flow velocity. The current bucket wheel assembly is made of plated brass. It employs six hollow conical cups that are hand formed from sheet metal and individually soldered to a brass, star-shaped frame. The finished unit is then plated. The frame is shaped so that a strut connects the apex of each cup to the outer diameter of the following cup around the frame.
There are several problems associated with the metal wheel bucket assembly associated with the current Price Type-AA fluid flow meter. First, due to the building process described above, it is difficult to maintain precise dimensional control of the parts of the assembly. In order to obtain an accurate fluid flow reading using the Price Type-AA fluid flow meter, the “cups” of the bucket wheel must be as close to identical in dimensions and position as possible. Second, the struts used to attach the cups to the center frame provide a poor response to vertically angled water flow. Third, the cost of the metal assembly, due to parts and hand fabrication is relatively high.
In order to address some of these problems, a plastic version of the bucket wheel assembly was developed and disclosed in U.S. Pat. No. 4,866,985. This bucket wheel assembly was made from polycarbonate or polyethylene plastics. It comprised six non-hollow, conical cups and a center disc that were injection molded as one piece. While this design addressed the cost issue noted above, the design performed poorly in comparison to the metal bucket wheel assembly. This design was found to under register velocity in field conditions because of its poor cosine response to vertically angled water flows. The poor cosine response was due to the solid cups. Due to these limitations, this metal bucket assembly is still used under most conditions today.
Therefore, it is desired to provide a bucket wheel assembly for use in a Price Type-AA fluid flow meter that is relatively low in cost and provides at least the performance of the metal bucket wheel assembly used currently.